Efficient Pb removal through the formations of (basic) carbonate precipitates from different sources during wet stirred ball milling with CaCO3

Highlights: • Solubility of CaCO₃ is greatly improved in the ball milling process. • Stoichiometric reactions between lead salts and CaCO₃ • Pb removal capacity up to 2065.8 mg/g • High selectivity in multi-metal solution • Low moisture of lead residues for easy filtration -- Abstract: Calcium carbonate (CaCO₃) may be used for lead removal. However, due to compact structure and high crystallinity of CaCO₃, the utilization of CO₃^2– is low and Pb removal only stays at the extent of physical adsorption and surface precipitation. In this research, a wet stirred ball milling process was introduced to induce nearly stoichiometric reactions between lead salts of nitrate, chloride or sulfate with CaCO₃ by consequently updating fresh surfaces of CaCO₃. The CaCO₃ could completely dissolve in the system for the removal of Pb²⁺ on the same chemical molar equivalent. The removal rate reached simply over 99% with the aid of ball milling, based on the precipitations in the forms of lead carbonate (PbCO₃) from soluble nitrate and basic lead carbonate (Pb₃(CO₃)₂(OH)₂) from the hardly soluble sulfate occurring in a very wide concentration range. The process offered a new path for the treatment of abandoned lead paste based on the conversion of PbSO₄ to PbCO₃ or Pb₃(CO₃)₂(OH)₂ as well as recycling of lead resources from multi-metal coexisting lead-containing waste solutions. These (basic) carbonates precipitates may be used as secondary resources, while achieving environmental purification.